Airplane radio equipment



Jam. 3, 1933. c. F. JENKINS 1,393,287

AIRPLANE RADIO EQUIPMENT Filed Aug. 23, 1929 Patented Jan. 3, 1933UNITED STATES TENT OFFICE CHARLES FRANCIS JENKINs oF WASHINGTON,nrs'rmcr or CiOLfiMBIA. ASSIGNOR T 0. FRANCIS JENKINS,.INC., orWASHINGTON, nis'rnIer OF COLUMBIA ninrnnnnwnnmo nomfmnnr I Applicationfiled August 23,1929. Serial 'No. 387,894.

This invention relates to radio equipment carried aboard an airplane,andhas 'forits principalobject a simple assembly of-parts which whollyavoids interference from the electrical equipment of the engine.Heretofore it has been customary in airplane-radio equipment (a) tosuspend a wire under the plane with a lead weight, a lead fish attachedto the free end there'ofto hold it steady, and as nearly vertical aspossible; or (b) to fasten the antenna to .a vertical mast carried bythe plane. (0)1Antennae have also occasionally been fastened along wingtip to tail structure. I

All such antenna locations have serious interference from engineignition system radiation. For this reason costly shielding of themagnetos, the spark'plugs and hightension leads must be employed toavoid ignition noises in the exposed antenna preventing voicereceptionaboard the plane, and seriouslyinterfering with code reception.

the leading edge of the wings, and-(d) from Electrical high-tensionradiation fromthe engine ignition system is spherically radiated; andenvelops the plane, but by exploration it has been discovered that thereexists a radiation-free zone aft of the plane. This probably resultsfrom absorption by the metal parts of the plane fusilage, creating anelectrical shadow, and an interference-free zone behind the plane.

Whether this theory is correct or not, it has been found that there isan interference free zone aft in the line of flight; and that if theantenna is held axially in this zone, no interference to radiosignalreception results.

In putting this discovery into useful service a shielded radio set ismounted in the plane, in any convenient place. The ground Wire isfastened to the metal work of the plane, acting as acoimterpoise. Theantenna lead-in end is run through a shield, the unshielded end of theantennaflying aft from the tail structure. The free end of the antennaor antenna wire has a very light weight drag attached thereto to keep ittaut. V

- This drag may be for example, a small celluloid ball, althoughpreferably a body of stream-line forinp A balsam-wood fish serves.-quitesatisfactorily. ,A rash with screw pitched fins thereon also assists inpreventing it' floppin-gin the :slip stream by. cause ing the fishtorotate rapidly inthe extended axis of {the wire. Of course a-swivel isemployed betweenthe Wire and the fish.

In the drawing herewith illustrating the invention, A is;;an airplan e,in which isra radio'set B. withan antenna G, attached thereto. On thefree end 'of the antenna a light weight drag E is fastened. The lead-inend of the antenna is shielded in a tube D.

The operation of the invention is so obviousto those skilled in theairplane-radio art as-to need scarcely more than-a brief description. I

:Whether the'an-tenna isthrown overboard after the plane in flight,aswas d'one in ap'plican-ts firstexperiments, or is unreeled from aspool until the. right length of antenna isfiying, is immaterial; 'ineither event the drag holds the wire taut in the electric shadow in .the"Wake of the plane, which is the object sought, namely, that the antennadoesnot pick up any radiationfrom-the ignition system ofthe en-ginej 1Incidentallythe antenna with a light Weight dragholdingit axially in theslipstream creates far less parasitic resistance than eithera dependingantenna or a mast supported antenna; a

:Alsothis location of the antenna permits the use of such a length ofWire as Willtune to theprimary of the broadcast frequency, which issamore efiicientmethod than the employinent of a short antenna tuned to aharmonic frequency.

Quite obviously it is easier, and far less expensive to shiel-dthe radioset than it is to shield the engineignition system; which latter alsogives unending trouble in engine servicing and repair. 7

lVhat I claim, is 1 1.. The combinationiWith an airplane hav ing a:metallic structure including an engine and consequent enginesystemzradiatiomby reason of which metallic .structure'an interferencefree. zone is created, of a radio set mounted on the .airplane'intherearofthe Li L) engine, and an antenna connected tothe radio set andprojecting from the airplane through the tail thereof to fly insubstantially a horizontal plane and axially of the plane behind theairplane and its engine within the interference free zonewhereby thereis prevented interference from engine ignition radiation withoutshielding the magnetos, spark plugs and high tension leads. I

2. The combination; with an'airplanehaving a metallic structureincluding an engine and consequent engine system radiation, by reason ofwhich metallic structure there is created an interference free zoneextending behind the airplane, of a shielded radio set mounted withinthe airplane in the rear of the engine, an antenna connected tothe'radio set and projecting from the airplane through the tail thereofto fly in substantially a horizontal plane and substantially axially ofthe airplane and behind the airplane and its en gine in the interferencefree zone whereby there is avoided interference from engine ignitionradiation, and means carried at the outer end of theantenna "to maintainthe same taut in said radiation-free zone'aft-of the airplane.

3. The combination with an airplane having a metallic structureincluding an engine and consequent engine system radiation, of

a shielded radio set mounted within the airplane in the rear of theengine, a tube in the airplane leading rearwardly from the shieldedradio set to and through the tail of the airplane, and an antennaconnected to the radio set and passing through said tube and shieldedthereby within the airplane and having its outer portion projectingtherefrom to 'fly unshielded in substantially a horizontal plane andsubstantially axially of the airplane'behind the latter and its engineand within aninterference free zone created by parts of the metallicstructure whereby there is avoided interference from engine ignitionradiation.

4. The combination with an airplane having a metallic structureincluding an engine and a consequent engine system radiation, of a radioset mounted within the airplane in the rear of the engine, and anantenna connected to the radio set and projecting from the airplane soas to fly in substantially a horizontal plane behind the engine andwlthin an interference free zone created by the metallic structurewhereby there is avoided interference from engine ignition radiationwithout shielding the magnetos, spark plugs and high tension leads. V

5. The combination with an airplane having a'metallic structureincluding an engine and consequent engine system radiation, of a radioset mounted on the airplane. in the rear of the engine, an antennaextending from the radio set to and beyond the tail of the airplane andunconnected with the tail, the portion of the antenna beyond the tailbeing the only portion thereof exposed outside the airplane and beingmaintained taut in a substantially horizontal plane substantiallyaxially of the airplane behind the tail of the airplane incident toforward movement of the airplane in fiightand being located within aninterference free zone created because of electrical shadows cast by themetallic structure and thereby rendered free of interfering disturbancesincident to engine system radiation. I

6. The combination with an airplane having a-metallic structureincluding an engine and a consequent engine system radiation, part ofsaid metallic structure creating an electrical shadow and aresultinginterference free zone, of a radioset mounted within the airplane in therear of the engine, an antenna located behind the engine and whollywithin said zone and connected to the radio set and having its outerend. projecting from the rear of the airplane to flyin substantially ahorizontal plane and substantially axially of the airplane and itsengine whereby there is avoided interference from the engine ignitionsystem, andmeans carried at the outerend of the antenna to maintain thesame taut in said substantially horizontal plane.

7 The combination with an airplane having a metallic structure includingan engine and a consequent engine system radiation, ofa radio setmounted within the airplane inthe rear of the engine, and an antennaconnected to the radio set and having its outer end projecting from therearof the airplane tofly in substantially a horizontal plane andsubstantially axially of the airplane and its engine to preventinterference from the engine ignition system. 7 Y

8. The combination with an airplanehaving a metallic structure includingan engine and a consequent engine system radiation, of

a radio set mounted within the airplane in the rear of metallicstructure that creates an electrical shadow in the rear of the, engine,an antenna connected to the radio set and having its outer endprojecting from theairplane only at the rear thereof to fly onlyin therear of the airplane and in a substantially horizontal plane during theflight of the airplane so as to confine the dispositionof the trailinan'- tenna in the radiation-free zoneaftcof the airplane and created by'said electrical shadow. r r

9. The combination with an airplane having a metallic structureincluding an engine and a consequent engine system radiation, whichmetallic structure castsfan electrical shadow aft that part of theengine system that produces said engine system radiation, of a radio setmountedwithin the airplane in the rear of the engine, and an antennawhich is located wholly within said electrical shadow, whichisoonnected; to the radio set,

and which has its outer end always disposed in substantially ahorizontal plane during the normal forward flight of the airplanewhereby the antenna during the normal forward flight remains in theradiation-free zone created by said electrical shadow.

10. In radio equipment aboard a tractor engine airplane having aninterference free zone aft the engine, an antenna located aft the engineand wholly within the interference free zone and approximately parallelto the axis of the fuselage of the plane.

In testimony whereof I have afiixed my signature.

CHARLES FRANCIS JENKINS.

